The present invention relates to a circuit and method for protecting an energy-storage device.
Energy-storage devices (ESDs) are used in numerous applications, particularly in portable electronic devices. A variety of types of ESDs have been developed to meet the energy density and power density requirements of various applications. These types include conventional batteries, fuel cells, conventional capacitors, and ultracapacitors.
In many applications, it is desirable to be able to recharge an ESD. Recharging the ESD places the device back in a state from which it can continue to power electronic devices, even after its stored energy has been used. Examples of rechargeable energy-storage devices include lead acid, nickel cadmium (NiCd), lithium polymer (Li-poly), lithium iron phosphate, lithium ion (Li-ion), and nickel-metal hydride (NiMH) batteries.
ESDs may be damaged if operated under extreme conditions. Either improper charging or discharging conditions may lead to damage of an ESD. Operation at excessive temperatures may also cause damage. For example, overcharging may cause electrolytic decomposition of a lithium-based rechargeable battery. Over discharging caused by a short circuit across the ESD may cause a large current to be drawn from the ESD, causing damage to the ESD. For some ESDs, even excessive discharging under normal loading conditions, resulting in a slow drop of the energy stored in the ESD, may deplete the ESD below a level at which it can be fully recharged. Operation of an ESD at an excessive temperature may also damage the ESD or be a signal of excessive load, which, in turn, may damage the ESD.
To protect an ESD during adverse operating conditions, protective circuits have been used to prevent adverse charging, discharging or temperature conditions from impacting the ESD.